1. Technical Field
The present invention relates to a polypeptide having an activity for targeting a heterogeneous polypeptide to a surface of cytoplasmic membrane, a nucleic acid encoding the polypeptide, a method for localizing a polypeptide on a cell surface, and a method for detecting the polypeptide or the nucleic acid. More specifically, the present invention relates to a polypeptide having an activity for targeting a heterogeneous polypeptide to a surface of cytoplasmic membrane, and a nucleic acid encoding the polypeptide, which are useful for constructing a protein expression system useful in analyzing functions of the protein; a method for localizing a polypeptide on a surface of cytoplasmic membrane, which is useful for detecting an enzyme, a peptide hormone, various growth factors, a cytokine, a chemokine, an antibody molecule, a complement molecule, a serum protein, a cell adhesion factor, a nucleic acid-binding protein, a neurotrophic factor, a receptor or a ligand; and a method for detecting the polypeptide or a glycosylated polypeptide thereof, or a nucleic acid, which is useful for functional analysis of a protein, a delivery of a cell expressing the polypeptide to a target site in vivo, preparation of an antibody against the polypeptide, preparation of a vaccine using the polypeptide as an antigen, a gene therapy of cancer by which the polypeptide, or the like is targeted.
2. Discussion of the Related Art
With the advancement in sugar chain biology in recent years, the findings concerning the structures and functions of sugar chains of glycoproteins have been accumulated. However, with regard to the structures and functions of O-glycans, i.e., which are so-called mucin type sugar chains, since a convenient analytic method for sugar chain structures has not been established, the analyses have been delayed at present.
In particular, there are only few reports on the biological significance of O-glycosylation of secreted proteins. For instance, there has been reported that O-glycosylation in a C-terminal tandem repeat sequence of rat pancreatic bile salt-dependent lipase regulates the secretion of the lipase. Also, it has also been reported that even in the above rat pancreatic bile salt-dependent lipase, a region rich in proline, glutamic acid, serine, and threonine [referred to as PEST region, Science, 234, 364-368 (1986)] masked by O-glycosylation, thereby resulting in the delivery of the lipase to the pathway of the secretion system, not the degradation system [Journal of Biological Chemistry, 272, 27353-27361 (1997)].
Furthermore, it has been reported that protein targeting to the apical surface of polar cells is prevented by inhibiting O-glycosylation by mutagenesis in the mucin-like sequence or the mucin box or by means of a metabolism inhibitor or the like [For instance, please see literatures Journal of Biological Chemistry, 275, 6566-6572 (2000) for sucrase isomaltase; Experimental Cell Research, 258, 184-194 (2000) for dipeptidyl peptidase IV; Journal of Cell Biology, 139, 929-940 (1997) and Journal of Biological Chemistry, 273, 30263-30270 (1998) for neutrophin receptor and the like]. However, in the above literatures, a sequence necessary for targeting to a surface of the cell membrane or a signal itself has not been specified at present.